Contact lenses have been used commercially to improve vision since the 1950s. Many current contact lenses are made of hydrogels formed by polymerizing hydrophilic monomers such as hydroxyethylmethacrylate (HEMA) and vinylpyrrolidone in the presence of a minor amount of a crosslinking agent.
Conventional silicone monomers are typically hydrophobic, making dissolution in aqueous solutions or hydrophilic solutions, such as e.g. poly(ethylene glycol)/poly(vinyl pyrrolidone) (PEG/PVP), difficult. That is, conventional silicone prepolymers prepared from conventional silicone monomers lack satisfactory solubility. For example, silicone prepolymers lacking polar silicone monomer residues (see, e.g., comparative example 3, infra), silicone prepolymers having too few polar silicone units (see, e.g., comparative example 1, infra), and silicone prepolymers having too many polar silicone units (see, e.g., comparative example 2, infra) are typically insoluble in PVP/PEG solution. Further, conventional silicone monomers having very low silicon monomer residue contents (see, e.g., comparative example 4, infra), while at least partially soluble in PVP/PEG because the total amount of silicone monomer is relatively small, can suffer from unsatisfactory oxygen permeability. Moreover, the polymerization of conventional monomers when forming molded articles (e.g., contact lenses) typically results in shrinkage, which may be as much as 20% by volume.
Therefore, there remains a need for methods and compositions that overcome these deficiencies and that effectively provide soluble materials that exhibit minimal shrinkage when forming molded articles and that also provide molded articles exhibiting satisfactory oxygen permeability.